1. Field of the Invention
This invention relates in general to electrically driven centrifugal submersible well pumps, and in particular to a gas separator for separating gas from the well fluid prior to reaching the pump.
2. Description of the Prior Art
Submersible well pumps of the type concerned herein are centrifugal and driven by a downhole electrical motor. A pump will have a large number of stages, each stage having an impeller rotatably driven within a diffuser. These pumps are used to pump large volumes of fluid, such as oil and water from wells.
Most oil wells will also typically produce some gas. If the gas is of sufficient volume, it can reduce the performance of the pump. In these circumstances, gas separators are mounted in the assembly below the pump and above the motor and the seal section.
One type of gas separator utilizes an inducer within a housing above intake ports to pump the well fluid. The inducer is a helical flight screw pump driven by the shaft of the motor. A rotatably driven guide vane mounts above the inducer to impart a swirling motion to the fluid. A rotatably driven rotor is located above the guide vane. The rotor is a cylinder having at least one radially extending blade or vane. The vane will impart a centrifugal force to the well fluid flowing through the housing. This centrifugal force separates the liquid components from the gas components because of difference in densities, with the liquid components flowing near the outer wall of the rotor, and the gas flowing in a central area surrounding the shaft.
A discharge member mounts above the rotor. The discharge member provides a passage from the central portion of the rotor to the exterior of the gas separator to discharge gas. The discharge member also provides a liquid passageway for the remaining portion of the well fluid to flow upward toward the intake of the pump.
The rotating rotor gas separators work sufficiently well. However, in some wells, considerable entrained sand is present in the well fluid flowing up from the well. The sand will be damaging to the rotating components in the gas separator, causing abrasion and excessive wear.
Another type of prior art gas separator, such as shown in U.S. Pat. No. 3,175,501, Mar. 30, 1965, J. T. Carle, does not use a rotating rotor. Rather, the separation occurs due to reverse flow as the upward flowing well fluid enters ports in the sidewall of the gas separator and flows downward to a single stage pump impeller. The change in direction results in a separation of a portion of the gas. The reverse flow separator is effective in wells that do not have high gas-oil ratios. The reverse flow separator, however, uses a rotating impeller at the base for drawing in the well fluid. The impeller is subject to abrasion due to sand, causing early failure.